Method for obtaining iron-free aluminum compound from clays



United States Patent METHOD FOR OBTAINING IRON-FREE -ALU- MINUM COMPOUNDiFROM CLAYS Stanley Tucker, Collingdale, Pa.

No Drawing. Application May 25, 1955 Serial No. 511,118

'5 Claims. (Cl. 23-102) This invention relates to the recovery ofiron-free .aluminum compound; from .clays'zand low grade bauxites.

While not-foundfree in nature, aluminum'is one-of the armost abundant of the earths elements, comprisingabout 728% of. the lithosphere. It is most ;often found asja asilicate, as sin clays. It is also foundwin feldspars (as .K Al SiO in cryolite (Na AlF ),and in bauxite asa hydrated aluminum oxide (Al O(OH) While some bauxite. of commercial value is found in the UnitedQStates, thebulk of the 'American aluminum industry relies on foreign sources.

At the present time high silica clays are not being commercially used as a source of this metal. The recovery of aluminum from bauxite by the Hall process and the' more :rnodern commercial methods, such as the -'Bayer process, comprises in each instance, an alkaline'recovervmethod,

,7 2,847,279 Patented Aug. 12, 1 958 A further object is the provision of an acid-type method for the separation of the iron and-aluminum components of a clay or high silica bauxite in which the separation iseflected at slightly acid or substantially neutral conditions.

Another object of the present invention is theprovision of a method for the recovery of pure iron-free aluminum compound.

A still further object of the present invention is the provision of a method-'forobtaining a source of pure iron.

In the'process of-the present invention a raw kaolin, such as a Georgiakaolin-containing about'0.-l'0% Fego although clays having higher or lower concentrationsof -mum roasting temperature varies with different clays;--too high-a roasting=temperature renders the clays insoluble infidil-ute acids, .too low a roastingtemperat'ure fails -to render the clay into a formwhichvmay be readily dissolved inaci'd.

Theroasted kaolin is then contacted :with acid. Pre'f- 'erably, the initial contact-is'with afdilute solution of a -strong minera1 acid, :such asbetween about 1 3 molar and requires. a raw material havinga loW-- silica content.

As a practical matter an excess of more than about 5 percent of combined silica, renders a bauxite undesirable fory-present day "alkaline. commercial aluminum recovery methods,- although;the so-called Combination Process .developed during World War, H can be-utilized for treating low grade bauxites containing .up .to. about ISw- 'eight gpercent silica. Even the combination process cannot-be used for clays, which normally contain a much high percentage of silica.

Acid processes for theseparation of alumina. from clays .andghigh silica-containing bauxites have been suggested, but have so far proved to beyimpracticable. Thus, ,While silica and even titania, maybereadily separated -from alumina, as both of these impurities are not dissolved by strong acids, such as sulfuric acid; it has not yet been commercially feasible to securea quantitative separation of iron oxidelfrom alumina by.prior suggested, acidprocesses.

Commercial aluminamust contain.lessthan0.05 percent iron oxide. Because of the chemical .similarityof properties between iron salts and aluminum salts, the-difficulty of this separation has prevented, an acid-type metho'd'from being adopted, although some acid-type methods have been suggested.

One acid-type method that has heretofore been pro- .posed contemplates the dissolution of-the iron and-aluminumacornponents of kaolin in a very concentrated solution-of hydrochloric acid, such as 6-molar hydrochloric acid solution followed by selective liquid extraction ,offlthe iron components with an organic solventwhich .is-insoluble in concentrated acid. The aforesaid-acid-type method -has-notyprOMedprac- ;tical for many reasons. Thus, not onlyisihydrochloric acid relativelyexpensive; but moreover, "it ;is;v highly corrosive to iron equipment and its use would require expensive and elaborate equipment.

An object of the presentginvention is the provision of an acid type method for the separation.ofthe ironwand aluminum components of a clay orl ig-htsilicabauxitein which substantially quantitative separation I between, .the 'iron and aluminum components may.,beietfected.

.solution of nitric acid.

The preferred acids ofmy invention are nitric-and sul- Pfuric,most preferably the former. 'Nitricacid is a -strong mineral acid, and-*is an oxidizingsagent that will convert ferrous ions to ferric ions. As will be more fully "derveloped 'below, the .present invention is of utility with :ferric. iron and the use of-nitric. acid assures that'theiron will be. in this-form.

The nitric acid concentration is not critical and.--may range. over a broad: range, asfromsubstantiallyzeronnor- -mal to '5 normal xand'beyond. A preferred range:isvOz l preferred, as they are .generally more expensivethana combination of non-halide. acids and halide salts. Moreover, halide acids are non-oxidizing-:acids, and-willmot convert ferrous to ferric ions.

Preferably, the roasted-clay is ;slurrie'd in the-nitric acidfora length. of time suflioientatozleachihe iron and aluminum components 'from' the clay. Silica-andtitania are both .substantiallyt insoluble in dilute nitric orsulfuric :acids and-may be readilyse-paratefd :therefromibyrfiltra- -tion,- as with; a filter presstor the like. ,Thcfifiltered silica and/or titaniamaybezdiscarded.

-It is essential for the purposes of this -invention:.t-h,at .prior to, or at thenime of the extraction, ,as.-explained below, -.a water-soluble .metal halide .salt, or a-watersoluble halide salt or other source of halide ions .which decomposeselectrolytically beraddedtto the leach liquor. I- have successfully employed a .variety of halide saltsand compounds. Amo ng.these are: chloride salts such ,as sodium chloride, potassium. chloride, ammonium chloride, .calcium chloride,=.barium chloride andlithium chloride; bromide compounds, such as sodiumybromide and potas- .-si,um,bromide; .-iodide salts such .as sodium io,dide.-and potassium iodide; fluoride salts lsuchi as sodium fluoride and ammonium bifiuoride. At the present ;time:calcium chloride is preferred, this salt comprises an excellent source of chloride ions, is readily dissolved in dilute nitric acid, and is low in cost. It is advantageous to add an excess of calcium chloride so as to leave undissolved salt, in order to insure saturated conditions.

Subsequent to the addition of the inorganic halide salt to the dilute acid, the leach liquor is passed to a countercurrent extractor or one or more batch extractors for separation of the iron component from the aluminum.

For the extraction of a nitric acid leach liquor containing dissolved iron and aluminum, a variety of oxygencontaining organic solvents, which are insoluble in water and which form complex chloride-containing salts with iron may be used, including water-insoluble esters, ketones, alcohols, ethers, aldehydes and organic acids. Examples of such compounds include amyl alcohol, ethylene glycol ethyl ether acetate, methyl amyl acetate, ethyl butyl ketone, acetophenone, diisobutyl ketone, 2-ethyl hexyl acetate, carbitol acetate, n-amyl alcohol, methyl amyl alcohol, nonyl acetate, and diisobutyl carbinol.

Halogen-containing organic solvents may also be used in the process of the present invention. Examples of such solvents include carbon tetrachloride, chloroform, phenyl fluoride, o-dichlorobenzene, etc.

The preferred solvent for the process of the present invention is methyl isobutyl ketone, and to a slightly lesser extent methyl butyl ketone. Thus, methyl isobutyl ketone and methyl butyl ketone possess a far higher selective activity for the dissolution of ferric ions in the presence of halide ions than other solvents. Moreover, neither aluminum chloride nor other soluble aluminum compounds are withdrawn from aqueous solutions by these solvents.

The solvent stream containing the ferric complex is easily separated from the aqueous stream containing aluminum, since these are substantially immiscible in one another.

By adding the water-soluble halide salt to the extractor, corrosion of equipment due to the formation of a substantial amount of hydrochloric acid is prevented. Thus, the ferric ions rapidly form a complex with the halide ions, and the oxygen atom of the organic solvent, which complex withdraws the halide ions from the aqueous solution.

I have determined that virtually a quantitative separation of iron using methyl isobutyl ketone may be accomplished from substantially neutral aqueous solutions containing no free hydrochloric acid in the presence of excess calcium chloride.

However, in the absence of halide ions, such as chloride anions, selective dissolution of ferric ions in methyl isobutyl ketone from a dilute nitric acid solution is not feasible. Thus, ferric nitrate is substantially insoluble in methyl isobutyl ketone.

Recovery of the solvent and separation of the ferric complex can be accomplished by first scrubbing the solvent with water and then crystallizing out the ferric salt, preferably followed by precipitation of the iron with alkali. By reusing the Water, loss of solvent due to water-solubility may be minimized. Pure iron which is free from contaminants usually found with iron derived from other sources may then be obtained by reducing the ferric salt with hydrogen. Alternatively, pure iron sulfide may be obtained by contacting the ferric salt with hydrogen sulfide.

The aluminum in the dilute acid solution may be sepa rated by crystallization or precipitation. The primary contaminants associated with the separated alumina will be any excess of halide compounds or ions not contained in the solvent complex. Such contaminants may be separated from the aluminum compound by conventional technique, or may remain in the aluminum compound during the electrolytic processing as a supplementing electrolyte to obtain pure aluminum.

,4 Example I Extractions in accordance with the present invention, except that halide ions were excluded, were conducted with solvent mixtures of methyl isobutyl ketone and isopropyl ether as the extracting agent in various proportions and with the concentration of nitric acid being varied from Zero to 8 molar concentration. "In the absence of halide ions, it was impossible to detect any extraction whatsoever of iron from nitric acid solutions in which iron was present in a concentration of 11.2 grams of iron per liter of solution.

Example 2 In each of the following experiments ferric nitrate was extracted by methyl isobutyl ketone from solutions of ammonium chloride and nitric acid.

HNO; Molarity 01 00110., Fe Cone, gmsJliter, Percent gins/liter Original Final Extracted It is seen that the addition of nitric acid increased the extractability of the ferric nitrate, but that this effect tended to level out.

Example 3 The relative efiicacy of calcium chloride on iron derived from ferric sulfate, ferric nitrate and ferric chloride was measured for aqueous solutions which were saturated with calcium chloride.

than other iron salts, when saturated calcium chloride is used, a quantitative separation may be achieved with both ferric nitrate and ferric sulfate.

Example 4 A natural Georgia kaolin (clay) was calcined in a mufile-type furnace and dissolved in nitric acid. Insoluble matter was filtered out. The iron content was extracted by methyl isobutyl ketone and halide compounds such as chlorides, bromides, iodides and fluorides.

The following amounts of iron were extracted by methyl isobutyl ketone on the addition of halide compounds to a solution of the clay in 5 normal nitric acid:

Percent wt. Halide Compound Added Iron Extracted Barium Chloride 10. 3 Lithium Chlorirln 99, 9 Sodium Bromide 99, 3 Sodium Fluoride 25. 0 Ammonium Biflnm-irla 0 Potassium Br 89. 3 Potassium Iodide 77. 5

Example 5 The following amounts of iron were extracted by methyl isobutyl ketone on the addition of halide compounds to a neutral (containing no acid) solution prepared by dissolving the iron compound in water.

Iron Compound Halide Compound Added Sodium Chloride Potassium Chloride The following amounts of iron were extracted by carbon tetrachloride on the addition of halide compounds to a solution prepared by dissolving iron and aluminum compounds in water (0.1 molar H 80 solution) Percent Iron Compound Halide Compound Added wt. Iron Extracted Ferric Sulphate Sodium Fluoride 77 Do Potassium Bromide 17.0

All of these examples represent only a single pass. If the passes are repeated the percentage of extraction per pass will remain substantially the same, so that quantitative removal of the iron can be effected with suificient passes of fresh solvent.

The present invention may be embodided in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

I claim:

1. A process for the recovery of an iron-free aluminum compound from a clay or like silicate mineral containing chemically combined iron which comprises contacting said mineral with a 0.1 to 5 molar aqueous nitric acid solution, dissolving iron and aluminum into said acid solution, filtering oil undissolved silica, adding calcium chloride to said acid solution in sufiicient amount to saturate said acid solution with such calcium chloride, extracting the iron from said acid solution by dissolving the iron in methyl isobutyl ketone, and retaining all of the aluminum dissolved in the nitric acid solution.

2. A process for the recovery of an iron-free aluminum compound from a clay or like silicate mineral containing chemically combined iron which comprises contacting said mineral with a 0.1 to 5 molar aqueous nitric acid solution, dissolving iron and aluminum into said acid solution, filtering off undissolved silica, adding a water-soluble inorganic halide salt to said acid solution in suflicient amount to saturate said acid solution with such water-soluble inorganic halide salt, extracting the iron from said acid solution by dissolving the iron in a ketone, and retaining all of the aluminum dissolved in the nitric acid solution.

3. A process in accordance with claim 2 in which the ketone is methyl isobutyl ketone.

4. A process in accordance with claim 2 in which the ketone is methyl butyl ketone.

5. A process for the recovery of an iron-free aluminum compound from a clay or like silicate mineral containing chemically combined iron which comprises contacting said mineral with a nitric acid solution, dissolving iron and aluminum from said mineral into the nitric acd solution, filtering oif undissolved silica, adding a water-soluble inorganic halide salt to said nitric acid solution, extracting the iron from said nitric acid solution by dissolving the iron in a water-soluble organic solvent consisting of a ketone, separating the iron-containing solvent, and retaining all of the aluminum dissolved in the nitric acid solution.

References Cited in the file of this patent UNITED STATES PATENTS 1,897,740 Teller Feb. 14, 1933 1,953,144 Wilson Apr. 3, 1934 2,249,761 Hixson et a1. July 22, 1941 2,376,696 Hixson et a1 May 22, 1945 FOREIGN PATENTS 246,827 Great Britain Dec. 9, 1926 

1. A PROCESS FOR THE RECOVERY OF AN IRON-FREE ALUMINUM COMPOUND FROM A CLAY OR LIKE SILICATE MINERAL CONTAINING CHEMICALLY COMBINED IRON WHICH COMPRISES CONTACTING SAID MINEAL WITH A 0.1 TO 5 MOLAR AQUEOUS NITRIC ACID SOLUTION, DISSOLVING IRON AND ALUMINUM INTO SAID ACID SOLUTION, FILTERING OFF UNDISSOLVED SILICA, ADDING CALCIUM CHLORIDE TO SAID ACID SOLUTION IN SUFFICIENT AMOUNT TO SATURATE SAID ACID SOLUTION WITH SUCH CALCIUM CHLORIDE, EXTRACTING THE ITON FROM SAID ACID SOLUTION BY DISSOLVING THE IRON IN METHYL ISOBUTYL KETONE, AND RETAINING ALL OF THE ALUMINUM DISSLOVED IN THE NITRIC ACID SOLUTION. 